Effect of Strain Rate on the Stress-Strain Behavior of Sand

Drained triaxial compression tests on crushed coral sand were performed from near-static strain rates to very high strain rates (up to approximately $1,800\%/\mathrm{s}$). Experiments were performed on dry, vacuum-confined axisymmetric specimens at two different confining pressures (98 and 350 kPa) and two different densities (${\mathrm{D}}_{\mathrm{r}}$ approximately 36 and 60%). A gravity drop weight loading system was used to generate high strain rates. High-speed film photographs of the specimen were taken through the flat sides of a square triaxial cell. By using digital image analysis techniques, strains were locally measured near the center of the specimen to obtain the most uniform assessment. Stress-strain relationships are presented. The following effects were observed with increasing strain rates: the elastoplastic stiffness increased significantly; the failure shear strength increased moderately; the axial strain at peak stress decreased significantly; and volumetric strains became more dilatant. Unusual behavior was observed at very high strain rates. Examples include the peak stress was not always associated with the maximum dilatancy rate and shear band inclination angle was noticeably reduced.